1. Field of the Invention
The present invention relates to a method of manufacturing a shoe for a compressor.
2. Description of the Related Art
A compressor, that compresses a refrigerant gas, is built into a refrigerating circuit that is used as a vehicle air conditioner or the like. For example, a known variable-displacement-type swash-plate compressor has a plurality of cylinder bores 91a formed in a cylinder block 91, as shown in FIG. 9. A piston 92 is accommodated in each cylinder bore 91a so as to be able to carry out a reciprocating motion. Further, a swash plate 93 is supported by a drive shaft, not shown, such that the swash plate 93 is rotatable synchronously with the drive shaft and is tiltable with respect to the drive shaft. A pair of shoes 94 are provided, on each side of the swash plate 93, between the swash plate 93 and each piston 92. As shown in FIG. 10, the upper surface of each shoe 94 forms a part of a spherical surface as a spherical surface portion 94a, and the lower surface of the shoe 94 forms approximately a plane surface as a plane surface portion 94b. A cylindrical portion 94c is formed in the middle between the upper portion and the lower portion via a round portion R.
In the compressor having the above structure, the swash plate 93 rotates synchronously with the drive shaft and makes an inclined movement with respect to the drive shaft, and a rotary motion of the swash plate 93 is converted into a linear reciprocating motion of the piston 92 in the cylinder bore 91a, via the shoes 94, based on the rotation of the drive shaft, as shown in FIG. 9. Suction, compression, and discharging of a refrigerant gas are carried out at the head end of the piston 92, based on these motions. During this period, the spherical surface portion 94a of each shoe 94 slides on the surface of a spherical surface seat 92a of the piston 92, and the plane surface portion 94b of the shoe slides on the surface of the swash plate 93. Therefore, the shoe 94 is required to have high size precision and small surface roughness in order to allow a smooth sliding action.
Conventionally, the shoe 94 has been manufactured according to the following process which includes a cutting step and a shoe forming step.
As shown in FIG. 11, a wire 70 comprising SUJ2 (JIS Japanese Industry Standard G4805), a high carbon chrome bearing steel, is provided. This wire 70 is cut into pieces to obtain cut pieces 71 in a cutting step S90.
The shoe forming step S91 is then carried out. In a forging step S91a, each cut piece 71 is forged with a forging die 95, that has a spherical cavity 95c comprising a lower die 95a and an upper die 95b, to form a sphere as shown in FIG. 12. As a result, an approximately spherical steel sphere 72 having a slight flash 72a is obtained, as shown in FIG. 13.
Then, in a flash removing (deburring) step S91b in FIG. 11, a flash (a burr) is removed by sandwiching the steel sphere 72 between two rotary casting boards, not shown, and by rotating the casting boards, thereby to obtain a flashless ball 73.
Next, in a heat treating step S91c, hardening and tempering are carried out to obtain a heat-treated ball 74.
In a grinding step S91d, the heat-treated ball 74 is ground with casting boards similar to those explained above and is ground with a grindstone, thereby to obtain a ground ball 75. The hard ground ball 75 obtained in this way can also be used as a ball of a rolling bearing.
Further, the ground ball 75 is annealed in an annealing step S91e, thereby to obtain an annealed ball 76 that has a slightly lower hardness than that of the ground ball 75 and that has no internal distortion.
Then, in a rotary grinding step S91f, the annealed balls 76 and a slurry are put into a rotary grinder, not shown, and are rotated together. As a result, the annealed balls 76 are brought into contact with each other, and are mutually ground. Gloss is added to these balls, and stains adhered to the surfaces of these balls are removed.
Further, in a washing step S91g, an ultrasonic cleaning is carried out to remove slight stains adhered to the surfaces. A visual inspection step S91h is carried out, and an anticorrosive is then coated onto the balls in an anticorrosive processing step S91i. As a result, a raw ball 77 having a true spherical shape is obtained.
In a pressing step S91j, the raw ball 77 is pressed to obtain a material 78 formed in a shoe shape.
Further, in a heat treating step S91k, hardening and tempering are carried out. Then, the shoe-shaped material is ground, to obtain a shoe shape and a surface coarseness within a standard, in a finish grinding step S91l. The shoe-shaped material is further cleaned in a washing step S91m, and is dried in a drying step S91n to finally obtain a shoe 94 for a compressor.
The conventional manufacturing method employs the flash removing step S91b and, therefore, the grinding step S91d and the rotary grinding step S91f are necessary. That is, as the steel sphere 72 is obtained in the forging step S91a by using the forging die 95 comprising the lower die 95a and the upper die 95b, it is difficult to obtain a desired shape, and therefore, the cut piece 71 having a slightly larger volume than that of a desired shoe is obtained so that the flash (burr) 72a occurs. As a slight gap is formed between the upper die 95b and the lower die 95a of the forging die 95, the flash 72a occurs in this gap.
According to the above conventional manufacturing method, however, the shoe 94 is manufactured from the raw ball 77, after the raw ball 77 has been manufactured. Therefore, many steps such as the forging step S91a, the flash removing process S91b, the heat treating step S91c, the grinding step S91d, the annealing step S91e, and the rotary grinding step S91f are necessary. In addition, as the raw ball 77 is completed through the above steps, and thereafter, the raw ball 77 is again subjected to the pressing step S91j that deforms the raw ball 77 to obtain the material 78 which is in turn subjected to the heat treating step S91l and the finish grinding step S91i. Therefore, an extremely large number of steps are carried out on the wire 70. Consequently, the process takes a long time, and is expensive.
The present invention has been made in the light of the above problems. It is, therefore, an object of the present invention to provide a method of manufacturing a shoe for a compressor that can shorten the manufacturing time and can reduce the manufacturing cost.
In order to achieve the above object, according to the present invention, there is provided a method of manufacturing a shoe for a compressor comprising the steps of cutting a steel wire to obtain a cut piece, and forming a shoe for a compressor from the cut piece, wherein, in the cutting step, the wire is cut so that the cut piece has a volume approximately equivalent to that of a desired shoe, wherein the forming step comprises the steps of sequentially forging the cut piece with forging dies having three or more cavities to obtain a shoe-shaped material, and finishing said material by at least a heat treatment to obtain the shoe.
In this method, after the cut piece is obtained by cutting the wire into the cut piece having a volume approximately equivalent to that of a desired shoe in the cutting step, the shoe is manufactured in the forming step comprising the forging step and the finishing step. Therefore, a heat treating step, a grinding step and an annealing step which are carried out in a conventional manufacturing method to obtain a raw ball can be omitted.
Further, according to this method, the cut piece is cut in the cutting step so that it has a volume approximately equivalent to that of a desired shoe, and the cut piece is sequentially forged with forging dies having three or more cavities in the forging step to obtain the shoe. Therefore, there occurs small distortion in the cut piece in each forging step, and the obtained material has a highly precise dimension and there is smaller occurrence of a flash. Therefore, the conventional flash removing process becomes unnecessary. The material is then heat-treated to obtain the shoe in the finishing step.
Therefore, according to this manufacturing method, it is possible to omit many steps, compared with the conventional manufacturing method, and it is possible to shorten the manufacturing time, with a reduction in a cost for equipment and goods. It is thus possible to reduce the manufacturing cost. As the number of processes is decreased, it is also possible to prevent wastage of energy since the number of manufacturing steps is reduced.